Systems of direct injection of fuel into the combustion chamber of an internal combustion engine are generally known. A distinction is made between homogeneous operation as the first mode and stratified operation as the second mode. Stratified operation is used in particular at low loads, while homogeneous operation is used when higher loads are applied to the engine. In stratified operation, fuel is injected into the combustion chamber during the compression phase of the combustion engine. As a result, there is no longer a uniform distribution of fuel in the combustion chamber. The advantage of stratified operation is that the applied smaller loads can be carried by the combustion engine with a very small amount of fuel. However, higher loads cannot be handled in stratified operation. In homogeneous operation, which is intended for such higher loads, fuel is injected during the intake phase of the engine, so that turbulence and therefore distribution of fuel in the combustion chamber are easily achieved. To this extent, the homogeneous mode corresponds approximately to the operation of combustion engines in which fuel is injected into the intake manifold in a conventional manner.
In both modes, i.e., in stratified operation and in homogeneous operation, the fuel injection time is calculated by a controller as a function of a plurality of input parameters so as to achieve an optimum value with regard to saving fuel, reducing exhaust and the like. The actual injection of the fuel then takes place at intervals determined by the predetermined angle of rotation distances. The angle of rotation distances are based on the crankshaft of the combustion engine in particular.
As a result, the actual fuel injection can take place only after the crankshaft has rotated by this angular distance, but not in between. For example, if the angle of rotation distance is six degrees, this means that the actual injection can always take place only every six degrees. Thus, the actual injection has an accuracy corresponding to the angle of rotation distance, i.e., an accuracy of six degrees, for example.
To achieve the above-described fuel savings in stratified operation, the calculated injection time must be maintained as accurately as possible. Thus, the accuracy of the actual injection must be as great as possible. This can be achieved by setting the angle of rotation distance corresponding to the intervals at which the actual injection can take place as small as possible. As a result, however, the controller must perform a greater number of computations because of the smaller angle of rotation distance, and thus the controller is under a greater load.
One of the objects of the present invention is to provide a method of operating an internal combustion engine with which the actual injection time can be maintained as accurately as possible.